1. Field of the Invention
The present invention relates to a control technique for a voice coil motor having a spring return mechanism.
2. Description of the Related Art
Digital still cameras, digital video cameras, or electronic devices (e.g., cellular phones) having an image sensing function include an actuator configured to perform positioning of a focusing lens. Known examples of such actuators include actuators using a stepping motor method, actuators using a piezoelectric method, and actuators using a voice coil motor (VCM) method.
A VCM is capable of generating driving power in a linear direction that corresponds to the direction of a current that flows through its coil. For example, in a case in which an H-bridge circuit is connected to such a VCM, such an arrangement is capable of switching the direction of the coil current, thereby allowing the driving power to be switched between the positive direction and the negative direction.
With applications required to have a small size, in some cases, such an arrangement employs a VCM having a spring return mechanism. A VCM having a spring return mechanism has a configuration in which the driving power in a first direction is generated by supplying a driving current to the coil, and the driving power in a second direction that is the reverse of the first direction is generated using the mechanical driving force generated by a spring attached to a mover. That is to say, such an arrangement uses both an electrical driving force and a mechanical driving force. In such an arrangement configured to drive such a VCM having a spring return mechanism, a driving current to be supplied to its coil is required to have only a single direction. Thus, such an arrangement provides a simplified driving circuit.
Miniaturization of electronic devices has involved an increased demand for providing a further miniaturized VCM having a spring return mechanism. With such a miniaturized VCM, the coil inductance becomes small, and the weight of its mover becomes small. This leads to a problem of oscillation (ringing) in the mover, i.e., the lens, due to the force generated by the spring.